Field of the Invention
The invention relates to a method and a solution for cleaning a container, in particular a boiler of a conventional power station.
Containers, in particular power station boilers, must be cleaned, especially before operating the power station. Such boilers frequently contain greasy residues and deposits of magnetite and lime which are to be removed.
A paper by Christian Rogmann entitled xe2x80x9cMetallentfettung in sauren Lxc3x6sungenxe2x80x9d [Degreasing Metals in Acidic Solutions] in Galvanotechnik 62 (1971) No. 7 discloses adding surfactants, which cause degreasing, to an acid which is used for removing rust from a metal surface. The solution used, which permits the combining of degreasing and pickling, is always acidic. An acidic solution of this type can cause parent metal corrosion.
A method for pickling metallic inner surfaces of closed vessels is disclosed by Austrian patent 281 541. This method is composed of three method steps. In a first step, termed pretreatment, wetting agents are introduced into the container. These wetting agents work to degrease the surface before the main treatment begins, so that the surface can then be wetted directly by a cleaning solution during the main treatment. The main treatment envisages the introduction of a mixture of complex-forming acids, hydrazine and cyclic amines, such that a pH between 3 and 5 is established by the amines and, if appropriate, by ammonia. The main treatment therefore takes place with an acidic solution.
A pH between 8.5 and 10 is not established until a subsequent posttreatment using volatile alkalizing agents. During that posttreatment, a thin magnetite protective layer forms on the container surface.
Heretofore it was also frequently customary to rinse the container with water between the individual cleaning steps. This is necessary in particular if the main treatment is a pickling with hydrofluoric acid.
It is accordingly an object of the invention to provide a method and a cleaning solution for cleaning a container that overcomes the above-mentioned disadvantages of the prior art methods and products of this general type, in which grease, magnetite and lime can be removed from the container in a simple and inexpensive manner, in particular, without the use of hydrofluoric acid, which is a hazardous substance (classification T, C).
A preferred ammonium EDTA salt is triammonium EDTA. Of many suitable surfactants a preferred example is the ethoxylated fatty alcohol surfactant sold by BASF under the tradename Plurafac. These compounds give an optimum cleaning result. This applies in particular when using the stated percentage compositions of the cleaning solution.
The advantage achieved according to the invention is that the method can be carried out considerably more rapidly than heretofore with the same cleaning result. This is possible, in particular, due to the fact that rinsing steps can be omitted. Since the cleaning solution is always alkaline, interfering parent metal corrosion cannot occur. Since only one method step is provided, not only is it unnecessary to drain the container between two steps, but also the specific feeding of chemicals for the individual method steps is unnecessary. Using only one method step, greasy residues and deposits of magnetite and lime can be removed without parent metal corrosion occurring.
The pH of the cleaning solution is suitably 8.5 or higher. Preferably, the pH of the cleaning solution is also 10 or less. An expedient pH is thus between 8.5 and 10. This ensures good cleaning without the risk of parent metal corrosion existing.